Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-02-22
2002-07-02
Cumming, William (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C370S229000, C370S318000, C370S332000, C370S333000, C370S335000, C455S436000, C455S442000, C455S453000, C455S522000, C375S377000
Reexamination Certificate
active
06415147
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a system for avoiding congestion in a mobile communication system, and more particularly to such a system which avoids a common communication line between a mobile station and a base station controller from being congested due to an increase in traffic, and resultingly, avoids degradation in communication quality in a mobile station.
2. Description of the Related Art
According to the IS-95 type mobile communication system standardized by U.S. Telecommunications Industry Association (TIA), when a common communication line of an asynchronous transfer mode (ATM) type is used in communication between a base station and a base station controller, a mobile station is designed to be connected to a base station through a wireless channel, and a base station is designed to be connected to a base station controller, which is a host relative to the base station, through a common communication line.
Voice signals transmitted between a mobile station and a base station controller are encoded in four rates of FULL, ½, ¼ and ⅛ in dependence on an amount of data included in voice signals in accordance with the variable rate voice signal encoding system defined in the above-mentioned IS-95 type mobile communication system. When a user makes communication, voice signals are encoded at a relatively high rate to produce a long voice frame, whereas when a user makes little communication, voice signals are encoded at a relatively low rate to produce a short voice frame.
The thus produced voice frames having a variable length are turned into ATM cells, which are transmitted between a base station and a base station controller through a common communication line.
When a mobile station is in soft-hand-off condition, that is, when a mobile station is in a condition to make communication with a plurality of base stations, a base station controller transmits the same voice frames in the form of ATM cells to all base stations to which a mobile station is connected, through each of down common communication lines. Voice signals transmitted from base stations to a mobile station are synthesized at the mobile station in wireless form.
Voice signals transmitted from a mobile station are turned into ATM cells in all base stations to which the mobile station is connected, and are transmitted to a base station controller through an up common communication line. Then, the ATM cells are turned back to voice frames in the base station controller.
When a base station controller receives voice frames having the same order numbers in the same mobile station, through a plurality of base stations, the base station selects a voice frame having best quality, and transmits the thus selected voice frame to a host apparatus.
However, if a common communication line becomes congested due to an increase in traffic, voice frames existing between a base station and a base station controller are all abandoned before being turned into ATM cells.
There have been suggested a lot of systems for avoiding congestion in a mobile communication system.
For instance, Japanese Unexamined Patent Publication No. 11-164346 has suggested a mobile communication system in which one of hard-hand-off and soft-hand-off is selected so that a ratio of mobile communication terminals carrying out hard-hand-off is increased in the mobile communication system, ensuring reduction in communication traffic between a wireless base station controller and a wireless base station.
Japanese Unexamined Patent Publication No. 11-275622 has suggested an apparatus for carrying out hand-off among base stations. The apparatus is equipped in a mobile communication exchange including a control signal line and a communication line both of which are connected to another mobile communication exchange. The apparatus is comprised of a first table in which a frequency at which the control signal line is used is stored, a second table in which a frequency at which the communication line is used is stored, means for finding a non-used line with reference to the first table, when requested by a base station to carry out hand-off, and finding a non-used line with reference to the second table, when a non-used line cannot be found with reference to the first table, and means for carrying out hand-off through the use of the thus found non-used line.
Japanese Unexamined Patent Publication No. 10-79985, which is based on U.S. Pat. No. 6,108,322 filed by Michael D. Cotzin on Jun. 28, 1996 and assigned to Motorola Incorporated, has suggested a method of monitoring a channel by means of a mobile unit in a communication system for transmitting data frame. The method includes the steps of monitoring a signal quality of a current traffic channel, judging whether the signal quality of a current traffic channel is within a predetermined level, ignoring data received by the current traffic channel during a time-slot assigned to the mobile unit for receiving data, and monitoring a control channel during a time-slot assigned to the mobile unit for receiving data.
Japanese Unexamined Patent Publication No. 10-145834 has suggested a method of carrying out soft-hand-off between a mobile station and a plurality of base stations in a mobile communication system including a mobile station and a base station to which the mobile station is connected, the method including the steps of connecting adjacent base stations to each other through a channel logically separated from a mobile exchange, and carrying out soft-hand-off control led by one of a plurality of the base stations, through the channel between the mobile station and a plurality of base stations.
Japanese Patent No. 2702437 (Japanese Unexamined Patent Publication No. 8-265818) has suggested a mobile communication system having a function of switching a communication channel. The mobile communication system includes a first memory storing a threshold value, a second memory storing a level of a received electric field in association with a base station which transmitted the electric field, and a comparator which, on receipt of a warning that a level of an electric field is degraded, compares the level stored in the second memory to the threshold value. If a level of the received electric field is greater than the threshold value, a request of measuring a level of an electric field is transmitted only to a base station associated with the level greater than the threshold value.
The above-mentioned conventional systems for avoiding congestion in a mobile communication system is accompanied with a problem that when an activity ratio of a common communication line between a base station and a base station controller is increased, and at last, becomes congested due to an increase in the number of mobile stations covered by a base station, voice frames existing between mobile stations using the common communication line and the base station controller are all abandoned.
The conventional systems are accompanied further with a problem that when voice frames of a mobile station which is in a non soft-hand-off condition and which is connected to a base station controller through a common communication line which is a sole communication line for the mobile station, are abandoned, voice data lacks between the mobile station and a base station controller, resulting in degradation in communication quality.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems in the conventional systems, it is an object of the present invention to provide a system for avoiding congestion in mobile communication which system is capable of reducing traffic in a common communication line and preventing degradation in communication quality in a mobile station using the common communication line as a sole communication line therefor.
In one aspect of the present invention, there is provided a system for avoiding congestion in mobile terminal communication, including (a) a plurality of mobile stations, (b) a plurality of base stations, and (c) a base station controller con
Hayashi Takanori
Ishii Toshitaka
Cumming William
NEC Corporation
Sughrue & Mion, PLLC
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